Quantitative and qualitative analyses of blood flow using continuous wave Doppler, pulsed Doppler, and Doppler color flow imaging techniques have become indispensable diagnostic tools in a wide range of clinical applications. However, the quality of information obtained from these techniques is severely compromised by two fundamental limitations: the ability to define only one projection of the three-dimensional blood velocity vector and, for the latter two techniques, aliasing. Our group has pioneered techniques and instrumentation that overcome these limitations and markedly extend the quality of flow data. Initial results indicate that two-dimensional vector flow (VF) techniques are capable of accurately quantifying velocities well beyond Doppler aliasing limits, along all directions within the imaging plane, without requiring Doppler angle estimation. In addition, initial in vitro studies have shown the ability to accurately quantify velocity profiles and volumetric flow rates in laminar vessels and jets, at flow angles of 90degrees where Doppler instruments fail. We propose to undertake simulation, in vitro, and clinical studies to examine novel vector flow techniques, based on parallel receive processing, that provide accurate, angle independent measurement of high blood velocities in clinically challenging applications. Specifically, we focus this research on quantification of regurgitant jets, in which high velocities and large flow gradients predominate. The performance of VF and Doppler methods of quantifying in vitro jet flow will be compared using a calibrated, computer-controlled phantom. These studies will include momentum and proximal flow analyses at clinically relevant velocities, noise levels, and turbulence. In addition, pilot clinical studies are proposed to investigate the performance of the VF methods in quantifying high velocity flow in mitral and aortic regurgitant jets, with comparison to continuous wave Doppler, the clinical gold standard for such measurements. It is hypothesized that VF imaging will increase the accuracy and ease of clinical measurements in such demanding applications and will provide consistent measurements regardless of the acoustic window utilized.